Zwitterionic amphoteric surfactant fire useful and versatile adjuncts in applications such as cosmetics, shampoo, detergents, industrial cleaners, emulsifiers, textile additives, aerosol packaging and the like. The prior art generally recognizes that such amphoterics can be prepared in accordance with the following reaction scheme. ##STR1##
For example, U.S. Pat. No. 2,195,974 describes a process for producing aminocarboxylic acids which comprises reacting acrylic acid or methacrylic acid with ammonia and/or organic derivatives of ammonia having at least one NH.sub.2 group at a temperature of between 40 and 150.degree. C. in the presence of water.
U.S. Pat. No. 2,816,911 discloses a process for preparing compounds of the formula: RNHC.sub.2 H.sub.4 COOR.sub.1, wherein R is an aliphatic hydro-carbon group containing 8-22 carbon atoms and R.sub.1 is a lower alkyl group containing from 1-4 carbon atoms. The process comprises reacting the corresponding amine RNH.sub.2 with the corresponding lower alkyl acrylate ester, said ester being employed in an excess of from 10-30% at temperatures within the range of 50-120.degree. C.
U.S. Pat. No. 2,468,012 discloses a process of producing a compound of the formula RNHCH.sub.2 CH.sub.2 COOX in which R is an aliphatic hydrocarbon group containing from 10 to 18 carbon atoms and X is selected from the group consisting of hydrogen and a salt forming radical. The process comprises reacting the amine, RNH.sub.2 with an ester of acrylic acid in the absence of a solvent and in the absence of a catalyst to form a beta amino ester, and replacing the ester group with a hydrophilic group.
Finally, U.S. Pat. No. 3,133,816 discloses the preparation of amphoteric surfactants by condensing at 25-30.degree. C., a primary amine containing from 8 to 20 carbon atoms with methyl acrylate to form the .beta.-alkylaminopropionate. The methyl ester is hydrolyzed to an acid or converted to the alkali or organic amine salts by the conventional method of saponification. The secondary amine is obtained by the use of molar proportions whereas the tertiary amine is obtained by using at least two molar equivalents of the acid derivatives.
Because of the special uses in detergents and cosmetics products, it is highly desirable that the surfactant have a low free amine content and a low free acid content along with good color. Further, it is known in the prior art that the performance of Zwitterionic amphoterics which contain one carboxyl group exhibit substantially different properties, i.e., hydrophobicity compared to those having two carboxyl groups, i.e., hydrophobicity. Thus, it is highly desirable to improve the state of the art by providing a process which allows for the preparation of amphoteric surfactants having low free amine content, low free acid content, good color, and low odor, which is selective thus allowing one to control the specificity towards one formation species over the other. In addition, the reaction of the primary amine and the alpha, beta-unsaturated carboxylic acid in an equimolar ratio does not exclusively produce one product, but results in a distribution of products, whereby the object of the present invention is to effect control over this distribution.
Accordingly, it is in object of the present invention to provide a process for the preparation of aqueous solutions of Zwitterionic amphoteric surfactants having low free amine and free acid content along with good color and odor.
It is a further object of the present invention to provide a process for the selective control of aqueous solutions of Zwitterionic amphoteric surfactant compositions depending on the end-use.
These and other objects are realized by the process of the present invention.